Studies in the applicant's laboratory have shown that, in the laboratory animal, fasting diminishes, and overfeeding increases central sympathetic outflow. Preliminary results indicate that, in the spontaneously hypertensive rat fasting or caloric restriction significantly diminishes blood pressure while overfeeding sucrose significantly worsens the hypertension. Studies in animals and man are planned to elucidate the mechanisms involved and to explore the possible therapeutic implications of caloric control (independent of sodium) in the treatment and prevention of hypertension. In the laboratory animal sympathetic activity is measured by determining norepinephrine turnover rates in peripheral sympathetically innervated tissues. In normal subjects and patients with essential hypertension sympathetic activity is assessed by the measurement of urinary and plasma norepinephrine.